Method and apparatus for eliminating narrow band interference by means of windowing processing in spread spectrum system

ABSTRACT

A device and method for eliminating narrow-band interference by windowing in a spread spectrum system are disclosed. The method comprises extracting N sampling points of data to perform frequency spectrum transform each time and obtaining N points of data; updating control information, comparing the energy values of the N points with the threshold within the set time period to determine the number of narrow-band interference as well as the width and location of the interference; determining the corresponding frequency domain adjusting window based on the width and location of the narrow band interference, obtaining the points within the window and the adjusted values of those points; with regard to the transformed N points during interference elimination process, setting the energy values of the points within the window during the current time period and the last period as the corresponding adjusted values, outputting the points after frequency spectrum inverse transform.

TECHNICAL FIELD

The present invention pertains to a method and device for eliminatingnarrow-band interference in a wireless communications, specificallyrefers to a method and device for eliminating narrow-band interferencein a spread spectrum communication system.

TECHNOLOGY BACKGROUND

Spread spectrum communication system is widely used nowadays. The spreadspectrum or the pseudo-random (PN) code modulation can reduce theinterference from other users and wireless signals. During thecross-correlation process of received signals and PN sequence, when theinterference is narrow-band signals, the interference signals willspread to the entire band and thus weaken the impact of theinterference. As a result, the spread spectrum signals can weaken thenarrow-band interference to some extend.

A typical spectrum of a spread spectrum signal (e.g. performing spreadspectrum from PN sequence) is submerged in the noise as shown in FIG. 1.An ideal signal is the signal energy that is actually sent out by themobile station and the noise is the additive interference. Obviously,the ideal signal energy of the spread spectrum is usually less than thenoise energy. “Strong interference” generally refers to the blockingsignals or the signals that are sent by TV, wireless station and nearbycommunication equipments. “Typical interference” refers to the signalssent by those low-power sources, such as amateur radio. Processing gainrepresents the interference signal levels tolerable by the spreadsignals in mobile stations. The spread signals can still be recoveredwhen they are affected by the typical interference, but they will neverbe recovered when the strong interference shows up. What's more, evenwith the typical interference, the signals can be recovered but thesystem performance will degrade.

Before utilizing CDMA communication system, the frequency band will beswept in order to protect the CDMA signals from the interference ofnarrow-band signals. However, since some burst signals are hard to befully forbidden due to the burst characteristic, the narrow-bandinterference will present disorder and randomicity. The narrow-bandinterference will increase the congestion rate and call-dropping rate ina CDMA system, as well as overload the radio-frequency power controlsystem, increase the power consumption of mobile station, and reducebase station coverage. Under extreme situation, the high-powerinterference will even block the entire cell, and thus the normalcommunication will stop. As a result, we must find a good solution inorder to eliminate the impact of the narrow-band interference signalspushing on the CDMA signals and guarantee a good communication quality.

Generally, the methods for dealing with narrow-band interference aredivided into two categories:

The first category is to make the signal (usually under analogprocessing) pass through a narrow-band notch filter or a filter group.This method is usually realized by the surface acoustic technology,which makes estimation for the frequency of interference signals andplaces the narrow-band notch filter wherever the narrow-bandinterference signals exist based on the estimation result. (PLL (PhaseLocked Loop) can also be used to track the narrow-band interferencesignals). However, the analog technology has its own limitations, andusually lacks flexibility.

Another category is frequency domain elimination which is generallyrealized through digital processing. Signals are first digitized andthen transformed into frequency domain through Fourier Transform. Thesedata will be processed in the frequency domain and finally betransformed back into the time domain to be output throughinverse-Fourier Transform. The methods for processing interferencesignals in the frequency domain can be concluded into two categories:the first method is to filter out the interference impact through thefilter on the frequency domain data and this method is suitable to thecase that the bandwidth and location of the interference are alreadyknown, but this method will have a certain limitation when the locationof the interference in the frequency domain, the bandwidth and thenumber of the interference are hard to identify, since there is acertain degree of difficulty in designing a fully adaptive filter.

Another method is to compute the signal amplitude on each frequencypoint and then compare them with a threshold value. The signalsexceeding the threshold values will be set as zero or be degraded tonoise level. This method can adaptively process multiple narrow-bandinterferences, multiple interference bandwidths and interferencefrequency changes. However this method only processes the data thatexceed the threshold, and in a practical system, the part of thefrequency spectrum with interference will leak to the neighbor frequencypoints because of some factors such as the selection for the number ofthe points of Fourier Transform. If the impact of spectrum leakage onthe capability for suppressing narrow-band interference is totallyignored, as the result, the capability for suppressing narrow-bandinterference can not meet the requirements of the system.

SUMMARY OF THE INVENTION

The technical problem that needs to be solved in present invention is toprovide a device and method for eliminating narrow-band interference byway of windowing in a spread spectrum system, reducing adverse impactsof spectrum leakage on the capability for suppressing narrow-bandinterference.

In order to solve the above technology problem, the present inventionprovides a method for eliminating narrow-band interference by way ofwindowing in a spread spectrum system, which comprises following stepsof:

(a) extracting N sampling points of data to perform frequency spectrumtransform each time, and obtaining N points of data;

Then performing control information update and interference eliminationprocessing respectively, wherein the control information updatecomprises the following steps of:

(b) for the N sampling points within a set time period, getting theenergy accumulation of data after transform for M times to obtain Nenergy values, comparing the N energy values with a threshold that iscomputed based on the these values, and then determining the number ofnarrow-band interferences as well as the width and location of eachnarrow-band interference, M≧1;

(c) determining the width, location and shape of corresponding frequencydomain adjusting window based on the width and location of eachnarrow-band interference, determining the points included in the windowand obtaining the adjusted value of each point;

The interference elimination processing comprises the following stepsof:

(b′) for the N points of data after frequency spectrum transform eachtime, based on the obtained points within each window and theinformation of adjusted value of each point during current time periodand the last period, setting the energy values of the data at thesepoints as the corresponding adjusted values and finally performingfrequency spectrum inverse transform for those adjusted values, thenoutputting them.

Additionally, the above method also possesses the followingcharacteristic: in step (b), said threshold value is obtained bymultiplying the minimum of said N energy values with a coefficient or itis obtained as follows: removing partial maximum energy values from saidN energy values and averaging the rest, then multiplying the averagevalue with a coefficient.

Additionally, the above method also possesses the followingcharacteristic: in step (b), if the energy value at a certain data pointis larger than the threshold, then this point is considered as aninterference point. Each group of consecutive interference pointsconstitutes one narrow-band interference, and the number of interferencepoints included in the narrow-band interference is considered as thewidth of this narrow-band interference by which the number ofnarrow-band interferences, as well as the width and location of eachnarrow-band interference in this data spectrum are determined.

Additionally, the above method also possesses the followingcharacteristic: in step (b), M is determined by the number of samplingcycles included in a time period, and this time period is of 60-120 ms.

Additionally, the above method also possesses the followingcharacteristic: in step (c), the shape of said window is determined inthe following way: with the prescient energy concentration degree of thenarrow-band interference signals, if the interference energy isconcentrated, then a window with a steep edge is to be selected; if theinterference energy is scattered, then a window with a slow-changingedge is to be selected.

Additionally, the above method also possesses the followingcharacteristic: in step (c), the adjusted values of the points withinthe window are set according to the noise level. The adjusted values ofinterference points are set as the noise level and the adjusted valuesof other points around window edge are set as the multiples of the noiselevel.

The device for eliminating narrow-band interference by means ofwindowing in a spread spectrum system provided by the inventioncomprises a frequency spectrum transform unit, an interferenceelimination unit, an interference elimination control unit and afrequency spectrum inverse transform unit, wherein:

the frequency spectrum transform unit is used to perform frequencyspectrum transform for the data of one-time-extracted N sampling points,obtain the spectrum of the data and output the transformed data into theinterference elimination unit and the interference elimination controlunit;

the interference elimination control unit is used to get N energy valuesobtained from energy accumulation of data after transform for M times ofN sampling points within a set time period, and compare the N energyvalues with the threshold obtained from these values, and then determinethe number of narrow-band interferences as well as the width andlocation of the interference based on the comparison result, choose onewindow for each narrow-band interference and obtain the information ofthe points included in the window as well as the adjusted values ofthose points, and finally output them to the interference eliminationunit;

the interference elimination unit is used as follows: for the N pointsof data after frequency spectrum transform each time, based on theinformation of the obtained points included in each window and theadjusted value of each point during the current time period and the lastperiod, it can set the energy values of the data at these points as thecorresponding adjusted values, which will finally be sent to thefrequency spectrum inverse transform unit;

the frequency spectrum inverse transform unit is used to performfrequency spectrum inverse transform for the N points of data outputfrom interference elimination unit and then output them.

Furthermore, the above device also possesses the followingcharacteristics: said interference elimination control unit furthercomprises an energy computation subunit, a threshold computationsubunit, an interference determination subunit and a window selectionunit, wherein:

the energy computation subunit is used to compute N energy values fromthe energy accumulation of data after transform for M times for Nsampling points within a set time period, and then output them to thethreshold computation subunit and the interference determinationsubunit, M is an integer which is ≧1;

the threshold computation subunit is used to compute the threshold forinterference determination based on said N energy values and then outputthe threshold to the interference determination subunit;

the interference determination subunit is used to compare said N energyvalues with said threshold, define the point whose energy value islarger than the threshold as the interference point (consecutiveinterference points constitute one narrow-band interference), determinethe number of the narrow-band interferences as well as the width andlocation of each interference, finally output the above information tothe window selection unit;

the window selection unit is used to select a suitable frequency domainadjusting window for each narrow-band interference based on thenarrow-band interference information output from the interferencedetermination subunit, output the information of the points within eachwindow and adjusted value of each point to the interference eliminationunit.

Additionally, the above device also possesses the followingcharacteristics: when said threshold computation subunit calculates thethreshold, it multiplies the minimum of said N energy values with acoefficient, or the threshold is obtained as follows: removing partialmaximum energy values from said N energy values and averaging the rest,then multiplying the average value with a coefficient.

Additionally, the above device also possesses the followingcharacteristics: when the window selection unit sets the adjusted valuesof the points within the window, it sets the adjusted values ofinterference points as the noise level and sets the adjusted values ofother points around window edge as the multiples of the noise level.

The present invention is targeted for eliminating the narrow-bandinterference in a spread spectrum communication system and it processesthe signals within the frequency domain. The employed narrow-bandinterference elimination processing method uses windowing processing tosuppress the data and it processes not only the data exceeding thethreshold, but the neighboring data as well. The method is very flexibleand it can also adjust the window shape according to differentinterference characteristics. The method of the present inventionweakens the impacts of the spectrum leakage on the capability forsuppressing narrow-band interference, thus efficiently improving thecapability for suppressing narrow-band suppression.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of the spectrum energy for general spreadspectrum signals.

FIG. 2 is a schematic diagram of the operation of the device forprocessing received signals in accordance with the embodiment of thepresent invention.

FIG. 3 is a schematic diagram of the notch processor in FIG. 2.

FIG. 4A and FIG. 4B are schematic diagrams of the shapes of two windows.

PREFERRED EMBODIMENTS OF THE INVENTION

The present invention will be further described with reference to thefigures and embodiments.

FIG. 2 is schematic diagram of the operation of the device forprocessing received signals in accordance with the embodiment of thepresent invention. It comprises a radio frequency converter 100, adigital quantizer 110, a digital down converter and processor 120, aninterference elimination device 130, and an automatic gain processor140.

The signals are received by the radio frequency converter 100 andconverted into digital signals after being sampled by digital quantizer110, then the signals are input to the digital down converter andprocessor 120 to become intermediate frequency (IF) signals. The outputIF signals will be input into the interference elimination device 130for interference elimination processing, and after the interference issuppressed, the data will be sent to the automatic gain processor 140for automatic gain control and finally be transmitted to the base-bandfor processing.

For the design of the location of interference elimination device 130,the device can either be placed before the automatic gain controller 140or at the place of base-band processing. In the present embodiment, itis chosen to be placed before the automatic gain controller 140. Thereason is that with the existence of the narrow-band interference, thesignal energy will far exceed the normal value and prohibit theautomatic gain controller 140 from performing ordinary gain control asit for non-interference signals, and when the interference is verylarge, it will be in saturation status and stop working. Therefore theselection of the location for interference elimination device 130 is akey factor in the design.

The above figure is only an example, and in fact other devices can alsobe added between individual devices.

FIG. 3 shows the diagram of the interference elimination device 130 inFIG. 2, and it comprises the following units:

a frequency spectrum transform unit 200 used to perform frequencyspectrum transform for the data of one-time-extracted N sampling points,obtain the data spectrum and output the transformed data into theinterference elimination unit and the interference elimination controlunit;

an interference elimination control unit 230 used to determine thenumber of narrow-band interferences as well as the width and location ofeach interference in a set period of time according to the comparisonresult between the N energy values obtained from energy accumulation ofdata after transform for M times of N sampling points and the thresholdthat is computed from these values, choose a window for each narrow-bandinterference and obtain the information of the points in each window andadjusted values of each point, finally output them to the interferenceelimination unit; the detailed calculation method will be introduced inthe following;

an interference elimination unit 210 used to perform windowing for the Npoints of data after frequency spectrum transform each time, based onthe obtained information of points in each window and adjusted value ofeach point during the current time period and the last period, set theenergy values of the data at these points as the corresponding adjustedvalues, and finally send the data after interference suppression tofrequency spectrum inverse transform unit;

a frequency spectrum inverse transform unit 220 used to performfrequency spectrum inverse transform for the N points of data outputfrom the interference elimination unit and then output them;

The interference elimination control unit 230 further comprises thefollowing parts:

an energy computation subunit 231 used to get N energy values obtainedfrom energy accumulation of data after transform for M times for Nsampling points within a set time period, and then output them to thethreshold computation subunit and the interference determinationsubunit, wherein M is an integer that is ≧1;

a threshold computation subunit 232 used to compute a threshold forinterference determination based on said N energy values and then outputthe threshold to the interference determination subunit;

an interference determination subunit 233 used to compare said N energyvalues with said threshold, define the point whose energy value isbigger than the threshold as the interference point (consecutiveinterference points constitute one narrow-band interference) anddetermine the number of narrow-band interferences as well as the width(represent by points) and location of each interference, finally outputthe above information to the window selection unit 234;

a window selection unit 234 used to select a suitable frequency domainadjusting window for each narrow-band interference based on theinformation of the narrow-band interference and prescientcharacteristics of narrow-band signals output from the interferencedetermination subunit, output the information of points within eachwindow and adjusted value of each point to the interference eliminationunit. Generally speaking, the adjusted values of interference points areset as the noise level and the adjusted values of other points are setas multiples of the noise level.

Based on the above interference elimination device, the method inpresent embodiment for eliminating narrow-band interference by means ofwindowing in a spread spectrum system comprises the following steps of:

step 1, extracting N sampling points of data to perform frequencyspectrum transform each time and obtaining N points of data;

then performing control information update and interference eliminationprocessing at the same time, wherein the control information updatecomprises the following steps of:

step 2, determining the number of narrow-band interferences as well asthe width and location of these interferences based on the result of thecomparison between the N energy values obtained from energy accumulationof data after transform for M times on N sampling points within a settime period and the threshold computed from these values, wherein M isan integer that is ≧1;

Accumulation can make the estimated result to be more approximate to thereal power spectrum and therefore reflect data characteristics moreactual. The duration of accumulation time period should, on one hand,guarantee the power spectrum obtained in the accumulation time period isstable, so the duration should not be too short, and on the other hand,guarantee that the characteristics of the narrow-band interference willnot change dramatically within this time period, so the duration shouldnot be too long. A period of 60-120 ms can be chosen.

When computing the threshold, it can be done by choosing the minimumwithin all the energy values and multiplying it with a coefficient of2-4, or by removing partial maximum values and averaging the rest, thentaking the value that is 3-3.5 times of the average value as thethreshold. Both of these two methods can avoid the impacts of excessivelarge energy values at narrow-band interference points on the thresholdcomputation. However the present invention does not define the thresholdcomputation.

If the energy value at a certain data point exceeds the threshold, it isbelieved that narrow-band interference exists at this point (representsthe frequency location) and it is called interference point in the text.Each group of consecutive interference points constitute one narrow-bandinterference and the number of interference points included in eachnarrow-band interference represents the width of the narrow-bandinterference.

Step 3, based on the width, location and characteristics of eachnarrow-band interference, determining the width, location and shape ofthe corresponding frequency domain adjusting window and obtaining thepoints included in each window, and also determining adjusted value ofeach point based on the noise level;

The width of frequency domain adjusting window is determined by thewidth of narrow-band interference. In the present embodiment, the widthof the window is chosen as 2-3 times of the interference width. Thewindow can be divided into a narrow-band interference part and fringeparts at each sides of the narrow-band interference. In order to keepboth sides symmetric, the differences (indicated by the number of thepoints) between window width and interference width should be even whendetermining the window width.

Sometimes, the characteristics of narrow-band interference (for example,the roll-off characteristic, amplitude) can be pre-determined, forexample, by the result of the spectrum scanner, it is to determinewhether its energy is concentrated or it has a steep edge. One way todetermine if the energy is concentrated or not is as follows: if theinterference width is equal to 1, then it is directly determined thatthe interference energy is relatively concentrated; if the interferencewidth is larger than one and the ratio of the maximum energy value tothe minimum of the interference is bigger than 0.707, then it also meansthat the interference energy is relatively concentrated; otherwise, itbelongs to the status that the comparison energy is relativelyscattered. All these determination rules can be set by oneself and thepresent invention is not limited to a certain rule.

The window shape is chosen based on the characteristics of thenarrow-band interference. If the narrow-band interference energy isrelatively concentrated, then the interference edge will be steeper,therefore, a window with a steep edge can be chosen; if the narrow-bandinterference energy is relatively scattered, then the interference edgechanges slowly, therefore, a window with a slow-changing edge can bechosen; if there are many types of interferences or the show-up time isuncertain, which leads to the unpredictable characteristics of theinterference signal, a window with the edge characteristics somewhere inbetween can be chosen. FIG. 4A and FIG. 4B give the examples of the twowindows. The FIG. 4A shows a reverse trapezoidal window, which is moresuitable for the situation where the interference edge is relativelysteeper. The window in FIG. 4B is more suitable for the situation thatthe interference edge changes slowly. The method for choosing windowshape based on the characteristics of the narrow-band interference canemploy the current technology.

When determining the adjusted values of the points within the window,the present embodiment sets the adjusted values of interference pointsas noise level, and sets the adjust values of other points around windowedges as the multiples of noise level, wherein the specific multipleswill be determined by the window shape; for example, when setting themultiples at the window base as 1 and the multiples at window top as 2,if the width and the shape of every part of the window are known, thenit can easily compute the relative value at individual point. The noiselevel can be obtained either by dividing the minimum within said Nenergy values by the accumulation times or dividing the average value ofthe rest energy values after removing the maximum ones from N energyvalues by the accumulation times. Other than that, we can use othercurrent methods as well.

After step 1, executing the following steps of interference eliminationprocess at the same time:

step 2′ for the N points of data after frequency spectrum transform eachtime, based on the information of the obtained points within each windowand adjusted value of each point during the last time period and currentperiod, setting the energy values of the data at these points as thecorresponding adjusted values, namely performing windowing for the areassubjected to interference, and therefore suppressing the interference;

When obtaining the window information for the current time period, M isusually set as 1. After taking out N points of data, the correspondingwindow information is computed based on these data and then windowing isperformed for these data, instead of using in the next round of dataprocessing. At this time, the data processing of the N points isperformed after the current window information computation. However onthe whole, the window information computation and data suppression areoperating in parallel. In the present embodiment, for the duration timeof narrow-band interference, it will not introduce adverse impacts whenprocessing the data of the next time period by using the windowinformation in the current period.

Step 3′, performing frequency spectrum inverse transform for theadjusted data, and outputting them as the data result, ending.

The purpose of present invention is to eliminate the narrow-bandinterference in the spread spectrum communication system and itprocesses the signals within the frequency domain. The employednarrow-band interference elimination processing method uses windowing tosuppress the data and it processes not only the data exceeding thethreshold, but the nearby data as well. The method is very flexible andit can also adjust the window shape based on the different interferencecharacteristics. The method of the present invention weakens the impactsof the spectrum leakage on the capability for suppressing narrow-bandinterference and as a result, efficiently improves the capability forsuppressing narrow-band interference.

Based on the above embodiment, the present invention can also performvarious modifications and changes, which should be within the scopedefined by the present claim. For example, when suppressing the energyvalues of the interference data, the values can also be set as zero,however, it will damage the original data greatly.

INDUSTRIAL APPLICABILITY

The present invention has already been realized in the cdma_(—)20001xbackward link. After the simulation, in the case of the existences ofboth large energy narrow-band interference and a plurality ofnarrow-band interferences, it greatly increases the suppressioncapability of the narrow-band interference suppression system andimproves the performance of the system. The present invention is acommon technology, and can be used in the technology for eliminatingnarrow-band interference in spread spectrum system.

1. A method for eliminating narrow-band interference by way of windowingin a spread spectrum system, comprising the following steps of: (a)extracting N sampling points of data to perform frequency spectrumtransform, in order to obtain N points of data after frequency spectrumtransform each time, wherein N is the number of the points and is anpositive integer; then performing control information update andinterference elimination processing respectively, wherein the controlinformation update comprises the following steps of: (b) for the Nsampling points within a set time period, getting an energy accumulationof individual data after transform for M times and obtaining N energyvalues, comparing the N energy values with a threshold that is computedfrom the energy values, and then determining the number of narrow-bandinterferences as well as width and location of each narrow-bandinterference, M≧1; (c) determining width, location and shape ofcorresponding frequency domain adjusting window and determining pointsincluded in the window and adjusted values of the points based on thewidth and location of each narrow-band interference; the interferenceelimination processing comprises the following steps of: (b′) for the Npoints of data after frequency spectrum transform each time, based onthe information of obtained points included in each window and adjustedvalue of each point during the current time period and the last period,setting energy values of the data at these points as the correspondingadjusted values and finally performing frequency spectrum inversetransform for those adjusted values, then outputting them; wherein instep (c), the window shape is determined as follows: with prescientenergy concentration degree of narrow-band interference signals, ifinterference energy is concentrated, then a window with a steep edge isselected; if the interference energy is scattered, then a window with aslow-changing edge is selected.
 2. The method in claim 1, wherein instep (b), said threshold value is obtained by multiplying the minimum ofsaid N energy values with a coefficient or is obtained as follows:removing partial maximum energy values from said N energy values andaveraging the rest, then multiplying the average value with acoefficient.
 3. The method in claim 1, wherein in step (b), if theenergy value of the data of a certain point is larger than thethreshold, then this point is considered as interference point (eachgroup of consecutive interference points constitutes one narrow-bandinterference) and the number of interference points included in thenarrow-band interference is considered as the width of this narrow-bandinterference and therefore the number of narrow-band interferences aswell as width and location of each narrow-band interference in this dataspectrum are determined.
 4. The method in claim 1, wherein in step (b),M is determined by the number of sampling cycles that are included in atime period, and the time period is of 60-120 ms.
 5. The method in claim1, wherein in step (c), the adjusted values of the points within thewindow are set according to noise level, it sets the adjusted values ofinterference points as the noise level and sets the adjusted values ofother points around window edge as multiples of the noise level.
 6. Adevice for eliminating narrow-band interference by way of windowing in aspread spectrum system, characterized in that the device comprises afrequency spectrum transform unit, an interference elimination unit, aninterference elimination control unit and a frequency spectrum inversetransform unit, wherein: the frequency spectrum transform unit is usedto perform frequency spectrum transform for the one-time-extracted Npoints of sampling data, obtain spectrum of the data and output the datainto the interference elimination unit and the interference eliminationcontrol unit; the interference elimination control unit is used to get Nenergy values obtained from energy accumulation of data after transformfor M times on N sampling points within a set time period, and comparethe N energy values with a threshold computed from these values, andthen determine the number of narrow-band interferences as well as thewidth and location of these interference based on the comparison result,choose a window for each narrow-band interference and obtain theinformation of the points included in the window as well as the adjustedvalues of those points, finally output the information to theinterference elimination unit; the interference elimination unit is usedas follows: for the N points of data after frequency spectrum transformeach time, based on the obtained information of points included in eachwindow and adjusted value of each point during current time period andthe last period, it sets energy values of the data at these points asthe corresponding adjusted values that will finally be sent to thefrequency spectrum inverse transform unit; the frequency spectruminverse transform unit is used to perform frequency spectrum inversetransform for the N points of data output from the interferenceelimination unit and then output them; wherein a shape of the window isdetermined as follows: with prescient energy concentration degree ofnarrow-band interference signals, if interference energy isconcentrated, then a window with a steep edge is selected; if theinterference energy is scattered, then a window with a slow-changingedge is selected.
 7. The device in claim 6, characterized in that saidinterference elimination control unit further comprises of an energycomputation subunit, a threshold computation subunit, an interferencedetermination subunit and a window selection unit, wherein: the energycomputation subunit is used to get N energy values obtained from energyaccumulation of data after transform for M times on N sampling pointswithin a set time period, and then output said N energy values to thethreshold computation subunit and the interference determinationsubunit, M is an integer that is bigger or equal to 1; the thresholdcomputation subunit is used to compute a threshold for interferencedetermination based on said N energy values and then output thethreshold to the interference determination subunit; the interferencedetermination subunit is used to compare said N energy values with saidthreshold, consider a certain point whose energy value is larger thanthe threshold as an interference point (consecutive interference pointsconstitute one narrow-band interference) and determine the number of thenarrow-band interference as well as the width and location of eachinterference, finally output the above information to the windowselection unit; the window selection unit is used to select a suitablefrequency domain adjusting window for each narrow-band interferencebased on the information of the narrow-band interference output frominterference determination subunit, output the information of the pointsincluded in each window as well as the adjusted value of each point tothe interference elimination unit.
 8. The device in claim 7, whereinwhen said threshold computation subunit computes the threshold, itmultiplies the minimum of said N energy values with a coefficient or thethreshold is obtained as follows: removing partial maximum energy valuesfrom said N energy values and averaging the rest, then multiplying theaverage value with a coefficient.
 9. The device in claim 7, wherein whenthe window selection unit sets the adjusted values for the points withinthe window, it sets the adjusted values of interference points as thenoise level and sets the adjusted values of other points around windowedge as the multiples of the noise level.